1. Field of the Invention
The present invention relates to a straight blade type turbine having a plurality of straight blades each disposed around a vertical axis and connected to a side of the vertical axis by a strut blade. The straight blade has a cross section with a solidity, a direction angle, a thickness, etc. which improves the turbine in an operational efficiency, an easy self start, and less noise.
2. Related Art
Recently, a wind power generation and a water power generation have been reevaluated in view of lower energy consumption and a national environment conservation.
Regarding a wind power generation, a wind turbine having a propeller with a horizontal axis has been mainly used. A propeller wind turbine has a better self starting performance without a specified starting device but has a directivity relative to a wind direction. Thus, the wind turbine requires a device which faces the wind turbine against wind. Furthermore, the propeller has disadvantageously a complicated profile which is difficult in a mass production thereof.
Furthermore, some wind turbines having a vertical axis and a plurality of vertically elongated blades have been utilized. A famous one of them is a Darrieus wind turbine which has a plurality of elongated blades with an arc profile around a vertical shaft.
A vertical axis wind turbine has no directivity against a wind direction so that it is suitable for a wind varying in seasons like in Japan. In addition, the vertical axis wind turbine has a simplified blade profile and is easy for a mass production thereof. The vertical axis wind turbine has an operational efficiency (output coefficient) equal to that of a horizontal axis wind turbine. Herein, the efficiency represents a ratio of an output (a torque multiplied by a rotational number) to an energy of wind. Regarding a vertical axis water turbine used in a water power generation, the efficiency represents a ratio of an output of the water turbine to an energy of a water.
However, the conventional vertical axis wind turbine disadvantageously has an extremely low self start performance, which requires various kinds of equipment such as a starting motor and a device for controlling the motor. Thereby, the vertical axis wind turbine requires such equipment increased in size and cost although it has blades simplified in the profile. Furthermore, the vertical axis wind turbine needs to have an improved profile of the blades to obtain a higher efficiency (output coefficient). The vertical axis wind turbine has a larger acoustic noise which must be overcome. These problems also appear in a water turbine.